This invention relates generally to a head slider of a magnetic recording drive, and, more particularly, to a head slider having an improved pad design so as to reduce bimodal stiction.
Disc drives are information storage devices that use a rotatable disc with concentric data tracks containing the information, a magnetic head or transducer for reading and/or writing data onto the various tracks, and an actuator connected to a carrier for the head for moving the head to the desired track and maintaining it over the track centerline during read or write operations. There are typically a plurality of discs separated by spacer rings and stacked on a hub that is rotated by a disc drive motor. A housing supports the drive motor and head actuator and surrounds the head and disc to provide a substantially sealed environment for the head-disc interface.
In conventional magnetic recording disc drives, the head carrier is an air-bearing slider that rides on a bearing of air above the disc surface when the disc is rotating at its operational speed. The slider is maintained next to the disc surface by a relatively fragile suspension that connects the slider to the actuator. The slider is either biased toward the disc surface by a small spring force from the suspension, or is self-loaded to the disc surface by means of a xe2x80x9cnegative-pressurexe2x80x9d air-bearing surface on the slider.
xe2x80x9cLoad/unloadxe2x80x9d disc drives mechanically unload the slider from the disc when the power is turned off, typically by means of a ramp which contacts the suspension when the actuator is moved, and then load the slider back to the disc when the disc has reached a speed sufficient to generate the air bearing.
In contrast to xe2x80x9cload/unloadxe2x80x9d disc drives, in a contact start/stop (xe2x80x9cCSSxe2x80x9d) disc drive, a flying head operated according to a CSS method is adopted. In the CSS method, the magnetic head makes contact with the surface of the magnetic disc surface during start and stop operations when there is insufficient disc rotational speed to maintain the air bearing. The head slider of the magnetic head is lifted up from the magnetic disc surface when the magnetic disc drive is in operation, the head slider flying over the magnetic disc surface due to an air flow on the magnetic disc surface generated by the rotation of the magnetic disc. The head slider flies according to a principle of a dynamic air pressure bearing at the magnetic disc surface. Therefore, the head slider of the magnetic head slides over the magnetic disc surface when the disc starts and stops. In this case, the read-write magnetic head device is attached to the head slider.
It is known that minimizing the head-disc spacing (HDS) is desirable because the amplitude of the read signal from the disc increases with decreasing HDS. Higher recording densities can thus be achieved.
To make the head fly, a convex portion is formed on a surface of the head slider facing the magnetic disc. Air flow causes a floating force to be generated in the convex portion and an air inflow region of the convex portion is formed in a taper shape. The convex portion is generally called a rail surface (or a flying surface). Before starting the operation of the disc drive or after stopping its operation, the rail surface of the head slider makes contact with the magnetic disc surface. Therefore, to prevent wear and/or damage of the magnetic disc surface, a protective film made of a hard material such as carbon or the like is formed on a recording layer of the magnetic disc. In addition, a lubricant layer is formed on the protective film to reduce friction and wear of the protective film, thereby improving the durability of the protective film.
If the disc has a smooth non-textured surface, the contact area of the magnetic disc with the head, when the head is rested in a stop condition, becomes larger compared to a textured surface. A very high static friction force, called stiction, (i.e., adhesion) between the head slider to the magnetic disc occurs, and a strength of the stiction increases due to an increased area of contact. The strength of the stiction has to be overcome in order for the disc to begin or resume spinning.
To suppress the stiction, it has been known to crown-process the head slider flying surface facing the magnetic disc along its longitudinal direction to decrease the contact area of the head slider with the magnetic disc.
Also, it has been known to deposit discrete pads, or projections, on the air-bearing surface of the head slider facing the magnetic disc. Theses pads or projections protrude below the level of the surface of the head slider to further decrease the contact area between the magnetic disc and the head slider. The height of the pads, also called xe2x80x9cSLIP pads,xe2x80x9d have to be accurately adjusted to have a stable operation of the magnetic disc apparatus when the flying of the head is started or stopped. Furthermore, the entire weight of the head slider rests on the pads which have a small surface. This causes large friction between the projection surfaces and the disc surface. As a result, the pads wear out rapidly.
The SLIP pads that have been designed so far have had limited success in solving one type of high stiction called bimodal stiction. Bimodal stiction is related to the tipping of the head slider on its rear edge. The bimodal stiction behavior of a classical head slider with SLIP pads, i.e. SLIP head, is characterized by a constant variation of the stiction force during a CSS test between a low value and a value that can be as high as several tens of grams. Also contributing to a very high stiction force is the formation of a large meniscus of the lubrication on the magnetic disc. FIG. 1 shows a schematic of the tipping mechanism and the formation of a meniscus contributing to the very high stiction force. As can be seen in FIG. 1, when the SLIP head tips on its rear edge due to the positioning of the SLIP pads, a large meniscus of the lubricant on the magnetic disc is formed between the magnetic head and SLIP head.
Accordingly, there is a need for a SLIP head that prevents tipping of the SLIP head on its rear edge in order to alleviate bimodal stiction. The design of the projections, i.e., contact pads, must also account for the curvature of the head (i.e., the crown and camber), preventing unintended contact between the air-bearing surface and the disc.
In accordance with the present invention, the above and other problems are solved by providing a magnetic head with a diamond-pattern directed tipping SLIP head which prevents tipping of the SLIP head on its rear edge by forcing tipping towards a corner. The design of the SLIP head then mitigates resulting stiction related to any corner tipping of the SLIP head. Furthermore, the diamond-pattern of the pads accounts for the crown and camber of the head, preventing any unintended contact between the air-bearing surface and disc.
The present invention SLIP head provides a design of the pads on the head slider in a diamond-shaped pattern. The diamond-pattern has four pads, or projections, positioned in a diamond shape on the head slider. Accordingly, one of the four pads is positioned on the longitudinal axis of the head slider, proximate the rear edge of the head slider. This pad positioned on the longitudinal axis, proximate the rear edge of the head slider, directs tipping toward one of the corners of the head, and inhibits direct rearward tipping onto the rear edge of the head slider.
The present invention also provides four additional pads, hereinafter called corner tip pads, on the head slider in a rectangular-shaped pattern. The rectangular-pattern, also having four pads, has each of the corner tip pads positioned near each of the four corners of the head slider. When tipping of the head slider towards a corner occurs, as directed by the diamond-pattern of the other four pads, these corner tip pads then prevent the formation of a large meniscus around the contact area. The corner tip pads also prevent line contact, which occurs when the longitudinal edge of the head slider is allowed to come into contact with the magnetic disc. Accordingly, due to the reduced area of contact between the head slider and magnetic disc, the reduced area of meniscus, and the permitted separation of the disc and head slider, the level of stiction is decreased.
In the present invention, the mechanism of back tipping and high stiction resulting from it is no longer random and unpredictable as with the classical SLIP heads. This results from tipping being forced towards the corner of the head. Knowing what direction the tipping will occur, the tipping to a corner can be controlled by the placement of corner tipping pads to control the formation of menisci. Furthermore, the head-disc budget concern, which is the separation between the magnetic disc and head, can be more easily addressed by modifying the rear pad location on the rear air-bearing surface and changing the pad heights.
In use in a CSS disc drive, the magnetic head, and attached SLIP head of the present invention, make contact with the surface of the magnetic disc during start and stop operations when there is insufficient disc rotational speed to maintain the air bearing. When this occurs, the diamond-pattern pads of the SLIP head of the present invention will direct any tipping to occur towards the corners of the SLIP head, away from the rear edge of the SLIP head. Consequently, this tipping will avoid the problem of bimodal stiction. Furthermore, by controlling the tipping and knowing in what direction it will occur, the strategically placed corner tip pads of the present invention will then prevent line contact and the formation of a large meniscus around the contact area.
While an embodiment of the present invention can be used in a magnetic recording device, it should be noted that the present invention could be adapted for use on other systems where stiction and its related factors as discussed herein are of concern. Such systems would include, for example, types of storage drives wherein a recording head comes to rest against a medium.
In sum, the present invention represents a significant improvement over the prior magnetic heads in many ways. The SLIP head in accordance with the present invention allows for directed tipping to avoid bimodal stiction. These and various other features as well as advantages, which characterize the present invention, will be apparent from a reading of the following detailed description and a review of the associated drawings.